Try it a few times and see how it goes. It's unique and original and likely something she hasn't heard before which can work in your favor.

She could counter with something such as "and I don't look good now?" Of course you could talk your way out of it if you get a chance, but it's going to put you off with a lot of girls in an awkward direction. Also, I don't think it's necessary to compliment their backside as an opener. I'm also not a big advocate of approaching from the back b/c it can startle them and they don't have a chance to see and evaluate you before the conversation. I've had women approach me from the back before and it startles me. You got 3 risky things there that can totally bust you. It can also overwhelm her b/c it's pretty outrageous.

Based on my experience, I never thought complimenting their physical appearance as an opener was a statistically high percentage tactic b/c the better looking women can be automatically turned off by it. When women compliment my looks it turns me off b/c I already know I'm hot. They are just stating obvious and boring stuff. Most likely if you have a situational opener, they won't be turned off but they are going to still realize you probably wouldn't have spoke unless you didn't think they were quality enough to speak too. so you still have the chance to transition it in to something more sexual within the frame work of the conversation.

I will have to disagree with this. the whole reason for this is for it to be a great neg that knocks her off her horse and makes her want your acceptance. And when you tap her, you are doing something called kino. even if its the very slightest amount, such as a tap on the shoulder, this kino is your "way in" to get more involved with the kino tactics with her.

I would also like to agree completely with what puaninja posted above.